1. Field of the Invention
This invention relates to a thermal transfer color printer capable of producing multicolored prints by using a thermal transfer printing ink ribbon, and more particularly to a full-color printer in which a sheet feed portion, printing portion and sheet discharge portion are arranged in the shape of a Y to increase the printing efficiency and performance and reduce the overall size.
2. Description of the Prior Art
There have been developed a variety of color printers such as an ink-jet printer and laser printer for obtaining a polychromic hard copy printed with an image corresponding to a colored visual impression produced on a computer display or the like. Of the color printers, a thermal transfer color printer has recently held a dominant position since it is excellent in size, handling, maintenance and picture quality such as color developing property and reproducibility. Typical thermal transfer color printers generally uses a thermal transfer ink ribbon coated with thermal transfer inks such as hot-melt color inks or sublimation-type color inks which are fundamentally composed of three primary colors of yellow, magenta and cyan. Occasionally, there is a case that black is added to the primary colors. The ink ribbon comes into close contact with a printing sheet such as paper so as to thermally transfer the color inks onto the printing sheet in turn by driving a thermal head having heating elements. That is, by carrying out the thermal transfer process for each of the primary colors, a desired image of full colors can be reproduced on the printing sheet.
For the purpose of heightening the ink transferring property and the coloring quality, an ink receiptor layer such as a binding or coating material for surface treatment is previously applied onto the printing sheet prior to printing, so as to make the surface of the printing sheet smooth and improve fixing of the inks on the printing sheet. The use of the binding material for that purpose is found in Japanese Patent Application Public Disclosures Nos. SHO 59-198196(A), SHO 61-83094(A), HEI 2-63892(A), and HEI 3-67665(A), and U.S. Pat. No. 4,660,051.
Further, U.S. Pat. No. 4,738,555 (corresp. to Japanese Pat. Appln. Pub. Discl. No. SHO 61-51391(A)) and U.S. Pat. No. 5,527,171 (corresp to Japanese Pat. Appln. Pub. Discl. No. SHO 59-95194(A)) disclose an after-treatment method for coating the surface of a printed sheet (hard copy) with a transparent protector layer to intimately fix the color inks on the sheet and prevent discoloration of the inks printed on the sheet.
Incidentally, it is technically impossible to apply the aforementioned ink receiptor layer and protector layer together on one ink ribbon. Thus, in order to provide the thermal transfer printer with both functions of effecting pretreatment for coating the sheet before printing with the ink receiptor layer and after-treatment for coating the printed sheet after printing with the ink protector layer, means for applying the ink receiptor layer and means for applying the ink protector layer should be prepared individually. However, since means for transferring the thermal transfer inks of three primary colors onto the printing sheet can be combined with either the pretreatment means or the after-treatment means, only two means suffice for the processes of effecting the pretreatment, printing and after-treatment.
In the thermal transfer printer using the three or more primary color inks, the color inks must be applied precisely to the identical portion on the surface of the printing sheet. Since the thermal transfer printer of this type causes the printing sheet being in contact with the ink ribbon to be moved relative to the thermal head, the printing sheet is required to be moved backward and forward at least three times relative to the thermal head. In the case of previously coating the printing sheet with the ink receiptor layer in the ink transferring portion of the printer, the backward and forward movements of the printing sheet should be carried out at least four times. However, the printing quality depends upon the registering of printing, and therefore, the relative positions between the printing sheet and the thermal head should be adjusted with a high degree of preciseness to ensure that the printed color dots on the printing sheet are in register.
Also in the conventional thermal transfer printer, the sheet feed portion from which the printing sheet is fed out, the printing portion on which the color inks are applied onto the printing sheet and sheet discharge portion to which the printed sheet is sent out are generally arranged in a line so as to move the printing sheet in one direction from the sheet feed portion to the sheet discharge portion through the printing portion. Accordingly, the printer necessitates the length equal to the total lengths of the sheet feed portion, printing portion and sheet discharge portion, and thus, it turns out to be large in size. Furthermore, since the protector layer applying means as noted above must be in actually added to the color printer of this type, the overall size, of the printer is inevitably increased, resulting in a greater possibility of failure of color registration (misregistration), and the resultant printing speed slows down.